There is a Torah commandment to procreate. With every child a couple has, they fulfill a great mitzva and partner with God in the creation of another human being (Nidda 31a), thereby sustaining an entire world (m. Sanhedrin 4:5). This is the primary goal of creation, as God wanted the world to be inhabited. The Sages declare, “The world was created only for procreation, as the verse states (Yeshayahu 45:18), ‘He did not create it to be empty; He formed it to be inhabited’” (m. Gittin 4:5).
However, if the mitzva would have no clear parameters, it would be too vague, and in many cases, due to a variety of concerns, it would not be properly carried out. Marriage is a sensitive and complex issue that depends on the ideas, emotions, hopes, and consent of husband and wife (and sometimes also on the financial and emotional support of parents). It demands responsibility and courage.
Even after marriage, the general mitzva leaves much uncertainty. On one hand, since a tremendous mitzva is fulfilled with the birth of every child, perhaps having one child is enough, for that child alone is an entire world. And perhaps the couple should therefore postpone having that one child until they are near the age of forty, when they are economically stable and have a wealth of life experience. On the other hand, given the importance and greatness of this mitzva, perhaps each person should make a superhuman effort to have as many children as they can – marrying as young as possible and shortening a baby’s nursing period to have as many children as possible.
The Torah therefore set basic mandatory parameters for the mitzva, in addition to expressing the general idea. The Sages provided additional parameters to give the general idea a clearer and more obligatory character. The general mitzva of the Torah is to “be fruitful and multiply,” and one fulfills the mitzva with each child born. The Torah obligation is to have a son and a daughter, just as God originally created Adam and Ḥava: “And God created man in His image, in the image of God He created him; male and female He created them. God blessed them and God said to them, ‘Be fruitful and multiply, fill the earth and conquer it’” (Bereishit 1:27-28). Since the verse makes it clear that the Torah wishes us to be fruitful, multiply, and fill the earth, the Sages established an additional obligation for a couple to have additional children (sections 5-6 below). They even determined a time for the fulfillment of the Torah obligation, that is, an age by which a person must get married (sections 7-10 below).
The general mitzva applies to men and women alike, and from a certain perspective, the woman’s reward is greater, for the more pain one experiences in fulfilling a mitzva, the greater the reward (Avot 5:23). However, there is disagreement about the individual obligation. According to the Sages, the obligation is incumbent upon a man; this is reflected in the man playing the more active role in effecting kiddushin and during sexual relations. It is also alluded in the verse, “Be fruitful and multiply, fill the earth and conquer it,” about which the Sages observe, “It is the nature of man to conquer, but it is not the nature of woman” (Yevamot 65b). Some explain that since pregnancy and childbirth are both painful and risky for a woman, the Torah did not impose it on women as an obligation, for “its ways are ways of pleasantness” (Meshekh Ḥokhma, Bereishit 9:7).
Yoḥanan b. Beroka disagrees with the Sages and says that women, too, are obligated in this mitzva, as the command is addressed in the plural, to both Adam and Ḥava: “God blessed them and said to them, ‘Be (pl.) fruitful and multiply, fill the earth and conquer it’” (Bereishit 1:28).
In practice, we rule in accordance with the Sages – the individual obligation is incumbent upon men. However, this does not diminish the rights of women; for instance, if it becomes clear that a woman’s husband is infertile, and she wishes to divorce him in order to have a child who will help her in her old age, her husband is required to grant her a divorce and pay her ketuba (Yevamot 65b; SA EH 1:13 and 154:6).
The practical difference is that if a woman does not want to get married, or wants to marry someone who cannot have children, she may do so; even though she is denying herself the opportunity to fulfill a great mitzva, she is not considered a sinner, since she is not obligated to procreate. A man, however, may not remain single and may not marry an infertile woman if he has yet to fulfill the mitzva to procreate (section 8 below).
As in the mitzvot of Torah study and prayer, here too we find that the Torah obligates men to fulfill the mitzva and makes it optional for women. As a result, those who are mandated and those who volunteer join together to fulfill the mitzva comprehensively.
The general mitzva, which is more important, applies to men and women alike, while the halakhic ruling that women are not obligated in the mitzva of procreation pertains specifically to the individual obligation of procreation. Therefore, when necessary, a Torah scroll may be sold in order to enable a woman to marry, just as it may be sold to enable a man’s marriage (MA 153:9; Eliya Rabba ad loc. 12; MB ad loc. 24; n. 21 below). According to most Rishonim (as explained below in n. 21), a Torah scroll may be sold to enable the marriage of even someone who has already fulfilled the Torah obligation of procreation. Since the general mitzva is unlimited, each and every child born fulfills this mandate, whether that child is an only child or a tenth child. This is the position of Ramban (Milḥamot Hashem on Yevamot 20a in the Rif pages) and Ha-elef Lekha Shlomo (EH 2). The general mitzva is also why a couple who have been married for ten years without children are instructed to divorce. If all that were at stake were the individual obligation, this would not be required. Therefore, if a couple has a son or a daughter, even though they have not fulfilled the individual obligation of having one boy and one girl, they are not required to divorce (6:7 and n. 8 below).
Some say that the verse at the end of the creation story (Bereishit 1:28) is a blessing, while the command was given later, to Noaḥ and his sons (ibid. 9:7). This is the position of Rashi, Ramban, and Tosafot. Others maintain that the verse at the end of the creation story is itself a command. This is the straightforward reading, as the dispute between the Sages and R. Yoḥanan b. Beroka (regarding who is obligated in the mitzva) revolves around this verse. This is the position of Sefer Ha-ḥinukh, Or Ha-ḥayim, Malbim, and Netziv. It seems reasonable to say that even the first position derives the basis for the general mitzva from this verse. I explain the foundation of this mitzva accordingly, in section 1 as well as here.